trace/ftrace.c

   1 /*
   2  * Ftrace trace backend
   3  *
   4  * Copyright (C) 2013 Hitachi, Ltd.
   5  * Created by Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>
   6  *
   7  * This work is licensed under the terms of the GNU GPL, version 2.  See
   8  * the COPYING file in the top-level directory.
   9  *
  10  */
  11
  12 #include "qemu/osdep.h"
  13 #include "trace/control.h"
  14 #include "trace/ftrace.h"
  15
  16 int trace_marker_fd;
  17
  18 static int find_mount(char *mount_point, const char *fstype)
  19 {
  20     char type[100];
  21     FILE *fp;
  22     int ret = 0;
  23
  24     fp = fopen("/proc/mounts", "r");
  25     if (fp == NULL) {
  26         return 0;
  27     }
  28
  29     while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
  30                   mount_point, type) == 2) {
  31         if (strcmp(type, fstype) == 0) {
  32             ret = 1;
  33             break;
  34         }
  35     }
  36     fclose(fp);
  37
  38     return ret;
  39 }
  40
  41 bool ftrace_init(void)
  42 {
  43     char mount_point[PATH_MAX];
  44     char path[PATH_MAX];
  45     int tracefs_found;
  46     int trace_fd = -1;
  47     const char *subdir = "";
  48
  49     tracefs_found = find_mount(mount_point, "tracefs");
  50     if (!tracefs_found) {
  51         tracefs_found = find_mount(mount_point, "debugfs");
  52         subdir = "/tracing";
  53     }
  54
  55     if (tracefs_found) {
  56         snprintf(path, PATH_MAX, "%s%s/tracing_on", mount_point, subdir);
  57         trace_fd = open(path, O_WRONLY);
  58         if (trace_fd < 0) {
  59             if (errno == EACCES) {
  60                 trace_marker_fd = open("/dev/null", O_WRONLY);
  61                 if (trace_marker_fd != -1) {
  62                     return true;
  63                 }
  64             }
  65             perror("Could not open ftrace 'tracing_on' file");
  66             return false;
  67         } else {
  68             if (write(trace_fd, "1", 1) < 0) {
  69                 perror("Could not write to 'tracing_on' file");
  70                 close(trace_fd);
  71                 return false;
  72             }
  73             close(trace_fd);
  74         }
  75         snprintf(path, PATH_MAX, "%s%s/trace_marker", mount_point, subdir);
  76         trace_marker_fd = open(path, O_WRONLY);
  77         if (trace_marker_fd < 0) {
  78             perror("Could not open ftrace 'trace_marker' file");
  79             return false;
  80         }
  81     } else {
  82         fprintf(stderr, "tracefs is not mounted\n");
  83         return false;
  84     }
  85
  86     return true;
  87 }